The National Map includes orthoimagery (aerial photographs), elevation, geographic names, hydrography, boundaries, transportation, structures, and land cover.
NHDPlus is an integrated suite of application-ready geospatial data sets that incorporate many of the best features of the National Hydrography Dataset (NHD), the National Elevation Dataset (NED), and the Watershed Boundary Dataset (WBD).
NHD+ V2 available for 1:100,000 NHD; high-res NHD+ in development
USGS and EPA contract Horizon Systems to build and maintain NHD+
How is the NHD+ made?
Some rules apply
Reaches are directed, and each reach has 0 or 1 inlet and exactly 1 outlet
NHD+ catchments are 1:1 for each internodal NHD reach
To generate the NHD+, 'hydroenforcement' is applied: Water must flow along flow lines
WBD is used to define the upstream boundary for NHD+ headwater catchments
Digital elevation is used to define NHD+ catchment 'walls'